1. Field of the Invention
This invention relates to radar apparatus, and more specifically to such apparatus useful in the location of underground pipes and other xe2x80x98buried assetsxe2x80x99.
For as long as utilities (pipes, cables, drains, etc.) have been laid underground the problems of thereafter detecting their location has existed. Very old pipes, such as water mains, for example, may have been laid decades ago when records were not kept and even in modem times, when the locations of laid utilities should have been well defined, the data are often found to be inaccurate.
When maintenance is required, or new utilities are to be laid, damage may be caused to the existing services by excavation. Recently there has been an increase in the amount of laying of such services with the advent of fibre-optic communications and, therefore, there is a strongly increased demand for accurate location information about all existing utilities laid along a pipe""s proposed route. Various types of locators have been in use for many years, however these, in general, yield only the surface trace of the utility, giving little or no information about depth, and such locators are not at all reliable where plastic pipe is laid.
2. Description of the Prior Art
Beginning about 25 years ago, short range or so-called xe2x80x98impulsexe2x80x99 radar was used for the survey of underground utilities. This is commonly known in the art as Ground Penetrating Radar (GPR). More recently the term Surface Penetrating Radar (SPR) has come into use although the terms are synonymous GPR is used in this document. GPR works as other radar systems, sending out short radio pulses and receiving the echoes following interaction of the signal with an object.
Acceptance of GPR use has not been very widespread amongst utilities survey organisations because previous and existing GPRs have been subject to a number of problems and disadvantages which will nova be considered.
Hitherto, all commercially available GPRs used for surveys of utilities have been systems which required the antennae to be in contact with the soil or surface being surveyed. The antennae are dragged or rolled along the surface to scan the area of survey. This requirement gives rise to significant difficulties if the surface is anything other than smooth or has obstacles thereon. In an urban environment, pavements and kerbs disrupt the xe2x80x98drag-scanxe2x80x99, while on greenfield sites, heavy vegetation or significant roughness, e.g. ploughed surfaces, may effectively rule it out.
Previous GPR systems for utilities survey have used radar systems which are comparatively narrow band. Thus, the typical frequency range which is used in such systems is of the order of ca. 100 to 1000 MHz. This range has to be covered by multiple antennae systems, wherein each antennae set, that is transmit and receive antennae, is specific to a particular range, for example a choice of 80, 120, 300, 450, 600 or 900 MHz for one common system. The problem with this approach is that the absorption of radar energy in the soil is crucially dependent on moisture content, with higher frequencies being very heavily absorbed by wetter soils. In general, one would like to use the highest possible frequency, so as to optimise the resolution of the image from the soil and its contents, i.e. the higher the frequency the greater the definition. This factor is dictated by the physics of wave transmission and the dielectric properties of materials.
With the narrow band systems currently in use, one is required to predict the soil properties and choose the appropriate antennae, so hopefully to yield the optimum result. However, if the soil is wetter than predicted, no echoes may be visible at all, necessitating a complete re-survey. Alternatively, if the soil is dryer than predicted, the highest possible resolution will not have been obtained. Therefore it is unlikely that the actual return signal will be sufficient for the purpose in hand and hence is very unlikely to have the optimal resolution.
Existing GPR systems for utilities survey mostly consist of at least two, usually three, separate units, interconnected by trailing cables. Thus, an antennae unit is connected to a controller unit, and usually to a recorder and/or separate power unit. This approach has obvious problems for portability and ease of use and, practically speaking, requires a crew of at least two for normal operation. Often, these heavy and excessive power-consuming units are placed in the back of a vehicle, but, in this case, the radius of operation is strictly limited by the length of the connecting umbilical cables. Moreover, when a system is provided as a single unit they are heavy, xe2x80x9clawnmowerxe2x80x9d type systems with ground contact antennae.
Typical GPR Systems currently in use produce either a low dynamic range paper record on a large and power-hungry recorder, or they produce an output on a CRT screen. Either display is at a unit remote from the operator who is actually scanning with antennae over the survey area. This means there is not an immediate feedback of the survey results to the operator. Typically, marks are manually placed an the record and these are correlated with surface features, more or less reliably, by the operator after completion of the survey. Furthermore, in conventional systems which have a near real-time display the display is cumbersome and has been found to be awkward to use.
Accordingly it is an object of the present invention to overcome or, at least, substantially reduce the problems associated with the prior art systems discussed above.
According to the invention there is provided a man-portable, non-ground-contacting, ultra-wide band impulse radar system, the system having separate transmit and receive antennae located in a common non-metallic housing mounted at one end of a lightweight boom, there being a data-processing computer and battery housing mounted at the other end of the boom and acting as a counterweight to the antennae system, and there being a data display and control unit mounted generally centrally of the boom, the boom being attachable to an ergonomic harness by which the whole may be carried by an operator so that the data display and control unit is in clear view of the operator, and having one or more handles by which the whole may be grasped and swung from side to side while being so carried.
Additionally, the system may comprise custom-designed miniaturised electronics and it provides a completely man-portable system with usage unlimited by weight, manoeuvrability or distance from power sources. By using xe2x80x9cair-launchxe2x80x9d antennae, it enables the radar radio waves to be transmitted through the air and then into the ground, it subsequently processes the received reflections and displays the data in very nearly real time, and by determining a phase difference in displayed hyperbolae, discriminates plastic pipes and their contents by detecting the interface between materials rather than the material itself.
Preferably, the antennae system comprises two copper leaves cut into complex, matching shapes and mounted at a precise angle and distance from each other. Each antenna may be a tapered impedance travelling-wave antenna using parallel-plate transmission lines together with a wide-band balun at the antenna input.
Furthermore, a radio pulse generator capable of providing a pulse covering, for example, the entire 100 to 1999 MHz band may be coupled to the transmit antenna, and a sampler may be coupled to the receive antenna. Additionally, the pulse generator may provide a monocycle pulse.
The sampler may possibly be a low-noise equivalent-time sampler, with a sampling unit being embedded in digital delay control circuitry, to scan that required delay range. Also, each of the generator and sampler may be mounted directly on its antenna and the data display unit may include a liquid crystal display device. dr
An embodiment of the radar apparatus in accordance with the invention will now be described by way of example only and with reference to the accompanying drawings in which;
FIG. 1 shows a side elevation of the ground penetrating radar system; and
FIG. 2 shows a block diagram of the components of the ground-penetrating radar system.